Development and passive exhumation of high-pressure shear zones (Blueschist Unit, Syros): Insights from quartz and columnar calcite microstructures

Quartz and columnar calcite microstructures in two major high-pressure (HP) shear zones (Syros Island, Greece), which carry meta-igneous rocks over calcite marbles, were studied to investigate the deformation conditions associated with their development and exhumation. Quartz-rich bands within the hanging-wall of the shear zones record the deformation during the operation of the shear zones under HP conditions at slightly decreasing temperatures (from 500 ? to 450 ?). At HP conditions, the shear zones are associated with (E)SE-directed shearing under plane strain conditions, as well as with a temporal increase in strain rate of one order of magnitude (from similar to 10(-12) to & nbsp;similar to 10(-11)). Well-preserved columnar calcite within marbles of the footwall indicates that ductile shearing along the shear zones should have abruptly ceased during the early stages of exhumation, passing to a period of relative quiescence within the stability field of aragonite at temperatures-430-450 ?. Progressive exhumation and cooling below 400 ?& nbsp;are associated with weak and distributed (E)NE-directed shearing with strain rate slower than similar to 10(-14). Our results from north(east) Syros indicate a change in transport direction from (W)NW-(E)SE at the deep subduction levels to (W)SW-(E)NE during exhumation. This change is linked to a change in deformation, from localized to weak and distributed revealing that the Blueschist Unit in north(east) Syros was exhumed as a nearly rigid body.

Automated summary

This study investigates the deformation conditions associated with the development and exhumation of two major high-pressure shear zones in Syros Island, Greece. The results indicate that the shear zones operated under high-pressure conditions, with a decrease in temperature and an increase in strain rate. During exhumation, the transport direction and deformation of the shear zones changed, revealing the exhumation of the Blueschist Unit as a nearly rigid body.